In a beta for a game like TD your only going to get a handful of the 1st few levels, iirc TD1 beta was only up to level 10, the point of these games is more the end game, so doubt you would get a good taste of what that would be like from beta tbh, but it might give you a general idea of the feel of the game, I heard they slowed it down a bit with needing to take cover for armour to refill, although that might just have been speculation.