Incursion is the game that's the whole reason why I talked about Monsters TD and Keeper of the Grove.
As I noted previously, each game made by this particular creator shows strong influence from the previous, with new twists each time that make for sudden significant improvements. The twist this time?
You don't build towers even though it's a tower defense game with guys going along a path as per usual. You man garrisons, by which I mean you choose a selection of guys to fill preexisting buildings.
While the art in this game is simple and cute (and genuinely so, rather than the overwhelmingly overdone attempt at cuteness from Keeper of the Grove), the gameplay is quite polished. I suppose when you have two other games to figure out what works and what doesn't, it's pretty handy to figuring things out.
When you select a garrison, you're given the choice of "hiring" one of three soldier types-the footsoldier type, the archer type, or the "sorceress" type. (The quotes are because there are frequent spelling inconsistencies, and furthermore all the soldiers are very clearly male and the magic users are usually called sorcerers.) The footsoldier is a melee warrior, while the archer and sorcerer are both ranged attackers (though they can enter melee combat, they're better off not doing so because they're not as tough and they do better damage with their ranged attacks). Once you've filled a garrison with three soldiers, you can buy upgrades for your guys in that garrison. If a soldier gets killed, he'll magically reincarnate after a little while.
Footsoldiers are a necessary part of your forces, because they're inexpensive and comparatively tough and because melee combat forces enemies to stop running, making them easier targets for archers and giving you more time to respond to them and for your ranged guys to do damage, but can't do anything against flying enemies. Archers are necessary because they do a lot more damage to certain enemies and are cheaper than sorcerers, especially when you start really climbing the upgrade tree. Sorcerers always hit a target when an enemy is on the screen, even if every single enemy in range dies before it can hit, slow whatever they hit down (both in movement speed and in attack speed for melee combat), and do more damage to most of the tougher enemies.
The balance between them feels perfect, to the point where multiple strategies feel possible. (Going for a lot of footsoldiers on early levels, then switching to a "meat shield/DPS" model-using a handful of footsoldiers to slow down enemies while pounding them with archers and sorcerers-works pretty well for most of the game.) You can mix and match guys for each garrison, though you'll usually want to stick with just ranged guys or just melee guys in one garrison. That your guys are moveable is a key to the game, as it means that each of your garrisons covers much more area than an otherwise comparable tower would. You can jockey your forces around, covering much more of the path than you might with either of the other games (and as I've noted, that's an important deficiency in those games).
One of the things in the game that's rather enjoyable is that each map after the first couple has something to make it unique. Occasionally, it's something unpleasant, such as a unique enemy, but usually it's a unique helper. Such as the tentacles in that lake.
The particularly unique thing about this helper is that you don't get money when it kills things, which is decidedly unhelpful of it. It also is completely random, only grabbing things when it darned well feels like it (also unhelpful, especially when it killsteals a low-health enemy you were about to get money from, even more especially because it instant-kills any enemy). Fortunately, most of the ally entities have better manners than that.
Sometimes, the helpers will actually be there to try to entice you to use your newly unlocked upgrades, perhaps most notably on a map where you have to deal with much larger than usual hordes of weak enemies, and there are a pair of Warhammers, big, tough melee guys whose attacks deal splash damage, hiding in the bushes towards the beginning of the path. They can die permanently, and they probably will when the nastier enemies start showing up, but for those first few waves, they're a blessing.
Within seconds of this screenshot, that dude with the big hammer (down towards the bottom, with the helmet with the red crest) turned around and killed at least half a dozen guys with one swing. That is how cool he is, and as of that level you get to fill an entire garrison with him if you want.
While each basic class has two upgrades that are pretty much "the same but more" versions of the starting version, after the second upgrade, each class splits into two lines, which are new and distinct from their predecessors and also have upgrades, and each upgrade has a new ability relative to its predecessor, capping off with powerful multi-talented soldiers capable of doing lots of damage. While I don't find the healer subclass very impressive myself, I've found uses for each of the others, and the Archmage at the top of the Battle Mage branch of the sorcerer line is the best thing ever (a single Archmage's chain lightning can stop an entire wave without significant help, and he's got a summoned buddy to do melee for him-there's one map where the best thing you can do is spend as much money as possible to get an Archmage as quickly as possible, and he plus your bonus help for that stage will take care of most of the early waves with little help).
Incursion retains the same spell structure as Keeper of the Grove, and even many of the same spells, with minor or completely insignificant changes to them. The biggest difference is that a spell that boosted your towers in Keeper has been replaced with a health regeneration spell in Incursion, and it's honestly one of the lamest things in the game, but I can live with that. It also has a similar skill point system to Keeper of the Grove's, with the added bonus of the skill points flowing even a little more freely and with some skill purchases being cheaper. (You can also cheat to get free skill points by liking the game on Facebook and such, but that's cheating.)
As I've suggested, Incursion shines on the front of its gameplay structure. This is all well and good, but does it keep up on that all-important front of the enemies you face?
Yes. Yes it does.
Incursion has a quite impressive array of enemies when you consider the number of levels in the game. The huge selection here isn't actually every enemy, either-there's one common enemy that isn't here for some reason, and there's also a boss sort of guy from one stage who doesn't show up here. But every other enemy, including the "final boss," is on this chart. There are a few of the "mainstay" enemy types that this creator clearly has a soft spot for, such as regenerating enemies, guys who turn invisible when hit for the first time, and guys who are specialized against certain of your guys (STILL HATEFUL AFTER ALL OF THIS TIME although this time it's considerably less cheap even though said specialist, the Antimage, kills your sorcerer-family soldiers in one shot from a distance and can deal good damage to any of your other soldiers), and a variety of other things, such as enemies that might respawn when killed, teleporters (much less cheap than you'd expect-in fact, they never got past me, anyway), guys who eat their buddies to regenerate, and more. The last stage, which you need to unlock by doing really well on the other stages and winning all the awards, actually has a bunch of unique enemies.
That final boss I mentioned? If he gets all the way down the path, you'll always lose immediately, because he counts as twenty guys instead of just one. (There are other enemies that count as more than one guy, but you get to find out which are which for yourself.) I got a little lucky my first time through, and had enough spells to paralyze him and keep him in one spot to be killed by my top-level archers and mages. Thus, I've seen the ending.
There are problems with Incursion, but nothing like the other games in this series. The economy is quite robust (you even make money from enemies that get past, which is handy), the gameplay is nuanced and balanced, and while it's a hard game, it's a fair sort of hard rather than being full of cheap shots. (I know it's fair because I managed to get to the last level, and that takes a bit of work.) On the other hand, some of the achievements you need to get to the final level are a bit forced (training lots of healers? No thanks), the guide is missing a few bits of important information such as the number of lives an enemy will take from you if it gets through, and there are a lot of comical typos, though that can be a plus if you're of the right mindset while playing.
My assessment is that if you like RTS games of a fantasy bent and don't mind the fact that it's about little chibi-esque guys murdering each other to death, leaving them to die in puddles of their own blood (no, seriously), this is a great game you should play. If you like tower defense games specifically, you should still consider it, though I can understand if you'd rather your defenders not be killable. (It's totally worth it, in my opinion, especially since they come back automatically for free, but your mileage may vary.) Even if you aren't particularly a fan of those things, consider trying it.
This is one of my favorite Flash games of all time, and it achieved that status shortly after I first started playing it.