I own the T490.
REGARDING OPENING OF THE CASE:
It is NOT hard to open, at all.
It is very easy if you have one of those small plastic phone opening tools with the little lip, or any little plastic piece to slide in between the crease and "pop" the case off. It's actually way easier to open than many other laptops. Seriously, disregard the complaints about that aspect, it's not a deal killer, at all.
Aside from that, the T490 isn't all that powerful as one might expect, and it is a little noisy, but it is super light. Screen response time is pretty slow and can be annoying (using WQHD).