Having given this game a second chance after a false start a few years ago (because Claptrap is bad), it's absolutely a worthy entry in the Borderlands series that I intend to revisit in the future.

Note: I played Nisha through 3 playthroughs of the main story, 2 playthroughs of Claptastic Voyage, and 1 playthrough of the Holodome. I also "speedran" TVHM, beating it in about 7 hours to get on to UVHM as fast as possible. I ended at LV62 with about 80 hours of Steam time or 2:14:00:00 in-game.

First of all, there's a lot of small additions, tweaks, and quality of life adjustments made versus Borderlands 2.
+ Stat scaling is sort of a hybrid of the systems from Borderlands 1 and 2. For example, starting damage/health/etc in TPS is closer to that of BL1 than BL2. You also level up at the same XP values in all three, but TPS is shorter than 2, so you don't level quite as far in each playthrough (and skill tree progression is tweaked as a result). This is a refreshing change (one of many) that keeps the game from feeling like a reskin.
+ Very very good class design with tons of depth. I played Nisha, and coming from Gaige in BL2, Nisha feels broadly similar to play, but with a way more nuanced skill tree. I could tell that there are tons of slightly different adjustments you can make to skill point allocation to tweak your skills to fit your loadout. As just one example, you could build Nisha with an Oz kit that focuses on improving gun damage, and consequently spec more into skills focused on fire rate, movement speed, and health regen.
+ Ultimate Vault Hunter Mode is noticeably easier than BL2, as enemies do not have health regen. It can be annoyingly challenging at times in BL2, so I welcomed this change.
+ The oxygen mechanic adds one more thing to keep track of, but generally speaking it's pretty easy to do so. This adds depth without feeling too annoying. Suffocation is rarely an issue in practical gameplay.
+ The grinder is a cool new way to deal with an excess of loot. I have some less positive things to say about it, but I'm glad it was added to the game, because it constantly changes how you approach inventory management, and can potentially make useless trash useful again. You may hold onto items 3-4 levels below your level in the case that you can get a high-damage blue or purple from the grinder. But, when you get to LV50+, you may only want to hold onto items 1-2 levels below, if that.
+ Although the item pool is smaller, there are some really cool new items, especially unique guns and shields -- Boomacorn, The Machine, MINAC's Atonement, E-GUN, Haymaker, etc. More thoughts on uniques later.
• The ability to mark an item as trash in inventory was removed.

Let's talk about low gravity...
+ On the one hand, it's fun to be able to jump long distances, and boost and slam as movement mechanics adds a whole new dimension to the skill ceiling. Mastering these skills can make combat way more fun!
• On the other hand, the map design can make it way too easy to die due to the low gravity. I will call out Triton Flats in particular. It's a nightmare for vehicles, as you can very easily run into bad geometry trying to jump over a chasm, fall into lava, and die. (And, even as a massive Borderlands fan, I have to admit that some of the geometry in these games is impressively bad.) Similarly, the Drakensberg can be really bad for being blown off a ledge into the abyss, or falling to your death from a jump pad.
• On the subject of map design, the extra distance you cover is counteracted by the more spread-out and larger maps. This can run the risk of making travel feel slow and cumbersome.
- It always feels bad when you kill an enemy and their drops get launched at Mach 5 into the void, especially when those items are mission items. For example, I had to relog into Stanton's Liver during one mission because a mission item was launched out of the map.

Now for nitpicks that stuck out during repeated playthroughs:
• A little too much dialogue that felt nagging or dragged the pace. Some missions I ended up outrunning the objectives of, because I knew where to go already.
• The raid boss is pathetic. I had never beaten a raid boss before because in BL1 and BL2 they're actually hard.
• The drop box for "To Arms" is located inside a bandit camp, so that means every time you deposit guns, you have to deal with a turret, a bunch of bandits, and potentially shugguraths. :(
• There are several Fast Travel stations that I would move or add, or one-way Fast Travels that I would make two-way, just for the sake of reducing the amount of travel. For example, the Outlands Canyon and Holodome stations are a bit out of the way. Furthermore, I really dislike the Veins of Helios, and the lack of a Fast Travel there contributes to that.

Other nitpicks.
• I think uniques are a little bit too common or overpowered. You can easily obtain Boomacorn and E-GUN, which together are a disgustingly powerful combination that can last for multiple levels. Don't get me wrong, they're awesome weapons, but they're a little *too* meta.
• The blue color of Oz is too similar to the blue rarity. You adjust to it, but it was annoying at first.
• The side missions on Helios feel like a drag at times.
• The level cap of 70 is too high to reach in normal gameplay, IMO. It requires grinding or a fourth playthrough.
• To avoid the RNG of the grinder, you may need to ALT+F4 over and over. This makes the game very unhappy. Sure, moonstones exist, but the cost of a moonstone grind is too expensive to justify doing it regularly. Also, there are combinations that you can't use moonstones with, so you're forced to bash your head against the RNG if you want a legendary.

9/10