Some time ago, I reviewed a game called Ghost Hacker.
Generally speaking, I was (and still am) pretty positive about this game; I think it's pretty great.
Ghost Hacker 2 has some things about it that are arguably improvements, but it also takes steps in directions I don't like at all.
The good: The enemy variety is still good, and while there's some filler in the form of "2.0" enemies that are just significantly powered up versions of other enemies, some of the new enemies, particularly this "Centipede," are improvements on similar enemies from the first game.
(Specifically and particularly, the Centipede is similar to the Medics and Reapers of the first game in how it works, sharing health instead of healing guys, but whereas the Reapers are slightly overpowered and the Medics are HELLA overpowered, the Centipede is perfectly balanced and more interesting to watch in action to boot.)
There are... less pleasant new enemies, but they're forgivable because they still are things that make you consider gameplay more carefully.
(I hate enemies that disable towers, but I must admit, the Glitches from this game are relatively fair, especially since one can put range boosters on the towers and keep them away from the creeps.)
Now, the bad: The towers are a distinct step down from the first game's.
They're mostly the same, but changes to the way they work take away from what made the first game unique. Primarily, whereas the first game required one to match colors of the upgrade points with the upgrades* (in order to encourage experimentation and use of different features than just cramming the same upgrade on four times), the game designers chose to use a variable cost system, where towers and upgrades cost more the more you use them.
Allow me to say that there is no system of encouraging use of diverse features that I hate more than I hate variable costing. The fact that the game gives you outside-of-normal-resources instants helps here, I suppose, and you can't actually lose material by recycling/selling stuff, but it's still terrible. (EDIT: Wow, for the longest time that was an incomplete sentence for no apparent reason. I must have been tired.)
They also added cooldown for the towers/upgrades in the pregame section. That also stinks.
This doesn't completely wreck the game for me, but I'm always going to think of it as "that screwy sequel."
*Admittedly, this system has problems, because it creates a lot of waiting for the colors to be what you want to be (they change at random while you've selected the tower and are waiting to place it). I appreciate that it has issues, but even the long wait is less offensive to me than the dumbing down and cost variability.