One of the games I've had sitting around unplayed for years on my Steam account is Tower Wars, which was on sale pretty cheap on the weekend and which apparently recently added a co-op multiplayer mode. Snuggles noticed this and picked it up so we could give it a spin.
Tower Wars is a pretty decent tower defense game using one of my favourite tower defense twists... The monsters aren't generated automatically over time by the game. Instead you play against another player and spend money to generate monsters to attack the other player. This was one of my favourite styles of tower defense games to play back in the WarCraft 3 mod days. It gives an extra dimension to the game where you need to decide if your money is better spent on defenses or on attacking the enemy.
Tower Wars has two types of currency. Gold which you earn over time and by killing enemy units and battle points which you earn by having monsters alive in your opponent's maze. You spend gold to make more towers or to make more monsters to send at the enemy. You use battle points to make your monsters better. You use both to upgrade your gold income rate or to unlock stronger units.
Because of the way you earn battle points (having your units stay alive longer in the enemy maze) it turns out making your monsters better and unlocking stronger units both serve to generate more battle points. It also has the secondary effect of forcing your opponent to spend his gold on more defenses or causes him to lose the game when he dies. There seems to be a real snowballing effect here, where if you get ahead and keep spamming units you end up earning enough battle points to upgrade your units enough that your opponent is stuck spending all of his gold on towers to stay alive and can't spend any gold on units to attack you. This means he doesn't earn any battle points and it means you don't need to buy any more towers. An early lead feels like a guaranteed win.
On the other hand, an even game feels interesting. When do you spend time to upgrade your gold income? Is it better to upgrade your units or unlock better units? There's a tech tree for upgrades and one for units and the way you go will change what towers your opponent needs to build since shields are hard to damage except for a specific tower that seems bad if they don't have shields.
I rarely find myself in an even game. Most of the time it feels like I get blown out, or I blow my opponent out. It actually reminds me a fair bit of playing StarCraft 2. The actual game, not any mod. It feels like some people have actual build orders for each of the maps and I get ruined by their tempo when I just randomly do upgrades that make sense. Knowing how much BP to expect against your opponent and knowing how large a wave you need to send in order to get the exact amount you need right now is probably a very important thing to know in a game with such a snowball factor.
Multiplayer against the AI doesn't seem to have the build units aspect. Instead it seemed to be a pared down tower defense game with an added twist where a big dude would periodically show up and destroy towers or chunks of land. This would impact your maze design temporarily or permanently. I guess it's good that it keeps you on your toes but I didn't find it terrible interesting.
You can also play a game with up to 3 people on each side where each player has their own tech trees and such, but share the gold income. I played a couple of 2v2 games with Lino but the queue times were really long and the games were blowouts in our favour. I'd like to give it a try against not randoms at some point.
Overall the game seems pretty reasonable. Hurray for whatever random bundle it came in!