Got my verson today, so far ive died 5-8 times and only 3 of those were by mobs the rest by falling down holes/stairs, think im near a boss battle as i just opened the big gate and a massive spear came flying out, not sure how well im going to do as im playing as a thief.
Yep the first boss is behind that door/gate

Pretty sure the Thief will be fine, but I'd expect he/she is better at ranged attack. Make sure you have Thief's ring now as I'm sure that will be a great help with your class.