Alien Invader (hacked version linked because I'm lazy) is perhaps the funnest rampage game I've ever seen.
I suspect it'd be a little less fun if I'd played the non-hacked version, where I presume you're more vulnerable and don't get to do some cool things as often, and are more subject to a time limit. But the core of the gameplay is probably pretty fun anyway because it's awesome.
Playing as a tripod is a thing I think I've seen once or twice before in browser games, but my hazy recollection tells me that none of them were this beautiful. I mean seriously, that's a nice tripod. (Reminder: There's no such thing as a "wrong" tripod, or as I put it elsewhere, every tripod is a "right" tripod. But there is a such thing as a great tripod, and this is definitely one of them.) But that only adds to the enjoyment that this game brings to the table.
See, just walking around as a tripod would be kinda boring. Fun at first using your heat ray or whatever to incinerate things and withstanding things with your shields (I don't know how effective they are because I can't be bothered to play the game without infinite health and shielding), but it'd get old quickly. The game designer(s) clearly knew this, because rather than restricting your abilities that way, they threw in a couple of things I've never actually seen attached to a tripod before, and they're actually brilliant choices.
First is a dash step that lets you move about a screen's worth of distance in about half a second, which is really cool to watch, fun to do, and pretty useful if you're actually in a hurry to complete the game objectives (it's also part of the reason I presume the cooldowns slow things down a lot, because with the hacked version I can finish a level in fifteen seconds or so thanks to the dash step).
Second and even better is the shockwave stomp, wherein your tripod can jump, and if you do the highest possible jump will come down and just make a frigging explosion with the landing.
The screenshot only brings across a little of the glory of sticking a landing in the midst of a small army and sending them all flying, but I'd recommend playing the game at least once just for that.
Anyway, after playing this game a little, I found myself thinking "this is the perfect way to spice up tripods if you feel the need to." Because, you see, tripods are a bit played out, even if they're still great when they're just kinda there. If you want to make your tripods more impressive than the baseline by making their assault capabilities scarier, rather than going with concepts built around realistic advancement in technology and the like, come up with superpowers and tack them onto the tripods. It's a lot cooler that way.
Regardless of my alien invasion-centered nerdery, this is a very fun game and I can recommend at least the hacked version. (And you can play the hacked version with the hacks off, FYI, so there's that.)