I love the TimeSplitters series. You get to go through all sorts of periods of time - from modern space times to ancient times - blasting away at the bad guys.
There are a ton of weapons available on each level, each more fun than the previous one. You can single and double wield depending on the weapon type. As you move along your route, you get checkpoints, to keep your progress going. There are enemies with invisibility cloaks, turrets to blast away from, and much more.
The comparisons with Halo are inevitable - especially in the modern time scenes. In many ways this is a great comparison, given how popular and well-designed Halo is. You get plasma grenades that stick to people, teammates that cover you, and generally good graphics. The cloaked characters give you just a hint of dark cloud to watch for.
The lead guy is very XXX-style and reluctantly goes on his time-hopping adventures. The voices are reasonably good - not great, but not really awful either.
The textures in the locations aren't great - but they're reasonable. There are details like worn wooden chairs and patches on the walls. The health and shield bars only appear when you're injured. I'd like it better if they were always on the screen in a corner, less annoying.
It's especially fun in co-op mode, taking on the bad guys with a friend. Multiplayer is great fun - the collection of maps is amazing, and you can even make your own!
Some of the dialogue is really funny, and in general it's a shoot-em-up game with a wide variety of weapon choices, locations and enemies. We enjoy this game greatly and play it quite regularly, even when we have many other games to choose from. It's comfortable and fun for all level of gamers.
Buy TimeSplitters 2 from Amazon.com