Great game!
I've not played team fortress 2, but i do like the look, and i'd love to play the engie. So to me, this game is awesome :D Though i notice a few problems.
1) shotgun doesn't work. maybe this is cuz i have a mac or some other odd reason, but i can't use the shotgun. i click and click and click on the opponents, and it doesn't work.
2)railroad achievement doesn't work. i think i actually tried using 1 sentry, no teleporters or dispensers. Lo and behold, nada.
3)"magic bullets" i notice at some ranges, sentry bullets pass through the enemy. while it can be annoying, i've used it to my advantage in taking out snipers unfortunate enough to be behind their matrix-impersonating comrades.
But, other than those three bugs, the game is excellent! If you make a sequel, it'd be fun to have the machines upgradable, or a few unlockables such as hats. (or perhaps alternate weapons to give valve ideas)
keep up the good work!