Naftak

Very addictive, modern take on Space Invaders, with Puppygames signature art style and soundtrack. Many different and generally tough combinations of enemies, you can upgrade almost everything to do with your ship (more firepower, faster firerate, extra weapons, smartbombs) between stages, of which there are 100.

Extremely fun, would recommend to anyone. If you enjoyed Revenge of the Titans, you'd be stupid to pass this up.

Everything about this game is amazing, especially the combat. Y U NO BUY

I think this is the best game, ever made. Ever.

One of the best tower defense games I've ever played, for sure. If you're a Portal fan, pick up the You Monster DLC with it. This game is immense amounts of addictive fun.

It should be a crime not to own and/or have played this game. It's amazing.

Calling it a 'game' seems like I'm not really covering the full picture, so I will recommend this as "an amazing experience". Some people love LIMBO, some people hate it -- but everyone should give it a try.
I'm yet to play anything like it.

Bought it, and found myself repeatedly coming back to it until I'd finished the story a few days later. It took me roughly five hours to complete on Easy.

Really addictive, old-school platformer action gameplay, the story actually ends up being pretty good, and keeps you playing to find out what happens next.

The soundtrack is AMAZING. AMAZING.

Also, worth pointing out that a mere few hours after completing it for the first time, I'm tempted to run through it again straight away. It is also worth noting there are four different endings.

Pretty sweet game. I'm not sure I'd have paid $10 for it in the first place (got it in a pack which more or less leveled its individual price to $2), but after playing it, I may have.
Very strange twist between RTS and Tower Defense. You have to go from city to city and evacuate it's occupants before the Zed infestation takes over. Every move you make impacts how the rest of the game will play out. For each civillian you evacuate and territory you reclaim, you get "Victory Points" -- get enough and you complete the campaign, but if you let things get even slightly out of hand and the Zed overtake you in VP, then you'll be desperately scrambling, trying to reclaim the lead.
Along the way, at certain VP targets, you'll unlock new ways of eliminating the Zed (some which result in you just levelling entire cities).
The more of a lead the Zed gets over you however, the harder the game gets, because they too unlock ways to overpower you in a similar fashion.

Fantastic game.

Play it with the lights off, your phone off, and headphones completely cranked at night.
It'll be the best money you spend in a long time. The tense atmosphere that this game builds up is incredible. I am yet to see another game do it better.

Everyone should play at least once.

Absolutely incredible game, played on Normal difficulty, took me 6 and a half hours to complete, and not even once was I bored or wanting to play something else. Still have the bonus campaign to play and developers commentary to check out too.
A real gem, don't miss it.

Amazing co-op game. Two players right now, but there's a promised 4-player co-op update coming soon! Perfect blend of FPS and Tower Defense.

One of the best shooters ever made. If you played it when it was around, you don't need convincing. If you didn't, you owe it to yourself as a gamer to pick it up and experience for yourself just how good this game is. It was fun in 1999, and it's still just as fun in 2011.

At first I really didn't agree with the physics and movement, but once you get used to it, this game is reasonably fun. Art style is gorgeous too. Buy it partly for a few hours of entertainment but mainly to support something new and creative.

Seriously, it'll be the best $10 you'll ever spend.