It's called a beta, but it's really more of a tech demo with some questing, mini-game mechanics and a small battle sequence to round it all off.
There's a crime system, stealth, horse riding, and archery. Melee combat obviously as well which underpins the entire game really.
RPG mechanics are present to an extent also, with some skill progression capability thrown in the mix.
If you're after a full game experience, the beta isn't for you. My advice would be to hold off for a bit, we're guessing we'll see a confirmed release date at E3 this year. So better to wait for the final game, than buy into the beta at this late stage... Cheers