I'm approaching Level 50 and explored half the map. I've been focusing on side quests and exploration somewhat more than the main quest, but with some new legendary weapons, power armor, and a hazmat suit, I think I'm ready to go into what's supposed to be the deadliest part of the map for the main quest.

I played two new race tracks for Accelerate and they were decent, but it was disappointing that I couldn't get in a race with more than 4 people. Perhaps it was because of the time of day I was playing it. This is really the type of game that needs at least 8 players to capture the same chaos and competitiveness of Mario Kart. Very glad they added Accelerate as a new game world though!

I got 8 main missions in but got stuck on a tough level and got tired of retrying the same type of levels.
The core gameplay loop consists of selecting/buying weapon components to put together, fighting robot/alien enemies in procedural rooms, more buying & crafting between enemy rooms, complete the level to get a mission reward and keep all loot. If you die then you lose all loot you brought, earned, or bought but keep your XP and unspent coins.  Progression early to mid game took me about an hour per main mission level, alternating between retrying main mission, doing XP missions, and a few free/pre-equipped missions.  
If you love FPS bullet hell, gun building is appealing, want co-op, and are good with procedurally generated levels, then this is a must buy game on sale.  If you don't have friends with this game and you often get tired of procedurally generated levels, then think twice about buying this game outright.

The main story/levels are more elaborate with special abilities and multiple lives, but as you progress you unlock some familiar things like endless mode. Its just as engaging as the first game, but more challenging in the later levels, where I might be stuck. I've unlocked the last area, but not everything on the second to last area. My advice is to not take certain powerups if you don't think you can use them strategically. That way, you will get better choices on powerups between levels.  The storyline (if you can call it that) is just as pretentious as the first one, which is okay with me, though it is somewhat creepier.

There was simply too much crafting at first for me to get into this, and I don't think I'm just saying that because I happen to be playing action packed FPS with moar action. There are lots of other games i'd rather play first, and I've not been keen on survival games with heavy crafting elements unless they have really engaging gameplay or environments (e.g. Subnautica).