Kaiji was a great series with it's first season. Not only is it's protagonist a relateable underdog, but the way he acts in the tough situations he's presented and how he shoulders the burdens of those who brought him this far truly makes him a great character. Moreover, it's good to see how he slowly develops his art of gambling, initially coming off as quite the noob before learning to fully analyse the game and work think with great tactics. To an extent, you could say Kaiji's like a more down to earth Joseph Joestar with far less plot armour. The setting is also quite interesting with how the rich treat the poor and working class as worthless, acting as a good allegory for the nature of gambling itself, as well as it's own commentary on social hierarchy. All the games within Ultimate Survivor were all interesting due to their complex rules or unique execution, be it a card game version of Janken or the E Card game. Moreover, the tense atmosphere and good visual symbolism help make you immersed in the climactic games completely. My only real complaint with Ultimate Survivor is the amount of time dedicated to the characters explaining their strategy to the most simplistic point, but that's a minor nitpick.
This praise is only really for the first season, Ultimate Survivor, since Part 2 is a very mixed bag. Whilst the initial game in the prison and the drama of Kaiji's struggle to even get a small amount of food were well executed, the 2nd season becomes boring when it essentially boils down to 15 episodes of playing Pachinko. The ending was decent, at least.
Haven't read the manga, seeing as how Part 3 isn't worth reading unless you have an in-depth knowledge on Mahjong. The ending of Part 2's anime was a good enough place to close on, anyway.
Part 1 - 8/10
Part 2 - 5/10
About a 7/10 overall.