Good questions all. Here are the answers plus some of my opinions.
Anyway is the difficulty is as high as BL2 like one-six direct hit equal down? I would say the bosses are on par, the general difficulty as about the same for first and second playthroughs but the third playthrough (UVHM) is not as difficult. UVHM badass enemies can be killer, several kills in fact if you don’t have the right approach.
Is the Cryo is still a must have like slag in BL2? Certainly not. They can be helpful with those badasses though (see above)
Are most of legendary really the same to BL2? Yes, the guns are the same with some different names with added legendaries for the laser type. New shields, grenade, oz kit and, obviously, class mod legendaries.
And I have heard someone from Steam review for something like there are bunch of death pit, is that true? If you mean slaughter pit like in BL1/2 then there is are two DLCs, one that came with preorder and one that is DLC. The latter is 5 rounds with the fifth round repeatable ad infinitum. It also adds new class mods and weapons.
One more thing. Is the environment in TPS is really that boring? I would not say they are boring but they do mimic BL2, a snow place, a flora/fauna area, a city like place, etc.
All in all, the game is just different. There are new classes so that makes it just fun to go through. There is the vertically of it all and the slam which change the gaming experience. A few new enemy types, new vehicles, and different humor. It is more of the same but a fun more if you ask my opinion, which I think you are. If you purchase, have fun!