I've played this game for over a year now and it's probably almost as good as a mario kart game, but there are some serious problems.
story mode is too generic. Basically Nolok kidnaps GNU and instead of eating him/her alive he decides to let Tux earn her back by beating him in a race? We never see him again until the final race. There are obvious problems with this:
1. Nolok is the only character to speak. What about a cutscene where Tux hangs out with some of his open source friends and then Nolok shows up.
2. Instead of Nolok being a fair creature, Tux should actually try to fight back (a get easily beat by nolok) and/or challenge him to a race in which Nolok accepts.
Final boss is too easy. Fort magma is the last track in the game so it's supposed to be the hardest track, but this track was one of the easiest ones in the game (even Cornfield Crossing is more difficult).
Maybe after beating nolok in a much harder track, Nolok still refuses to release GNU and then Tux finds himself in a boss fight against Nolok (in a 3 lives battle arena modeled after Fort Magma) in which the player must actually battle Nolok using items. Depending on which difficulty the player selects, Tux could have only 1 life (in the hardest difficulty) when Nolok has 3.
As for the 21 tracks in the main game, most of them are just ok. Some tracks such as Black Forest and Cocoa Temple are well designed but most of the older tracks feel like they need to be revamped. The worst tracks are Fort Magma (no explanation needed), Shifting Sands (very boring, terrible background, music could be much better), Snow Peak (poorly designed with terrible graphics and broken reverse mode), and Volcano Island (way too long with terrible textures and nothing exciting about the track. The part inside the volcano doesn't even feel dangerous at all and overall this track just feels like a clone of Gran Paradiso Island).
Other than Black Forest, none of the tracks really stand out or provide something original or creative. Some tracks like Oliver's Math Class are just failed attempts at trying to create something new. Minigolf is one of the better tracks in the game, but it's obviously outdated in terms of graphics, just like over half of the tracks in the game. I saw Alayan's thread on revamping tracks for 2.0. He said something about bringing Paradise Peaks to the main game, which I think would be a good idea since it's one of the best Addons tracks. I think Lost Chasm could also be a decent track for the game. I think Voclano Island needs to be completely redone since it's the most poorly designed track in the game (in my opinion).
Addons aren't much better, but at least this game has them (a feature which Mario Kart still doesn't have). Skindoormimiz tracks suck. They are all poorly designed and some of them are literally ripoffs of actual Mario Kart tracks (Shipyard Tower copied Airship Fortress from MKDS). There are some good tracks like Paradise Peaks, Lost Chasm, Green Hill, China, Industry, Nostalgia, High in the Sky, and The Cube.
AI does not seem to give a shit about you. I cannot count how many times I was doing well in a race, then some AI racer just decides to stop right in front of you, forcing you to a complete stop. The AI could have won that race but instead chose to sacrifice any chance of their victory just so they could see you lose. They must really hate you for them to do that.
Those are all the problems I can think of right now.