1. There are a lot of glitches between all versions of the game. It's not very game breaking, but it can be bothersome from time to time. A lot of the glitches happen either because you have to go out of your way to make it work (like the time trial videos by MilsTailsPrower on youtube) or it can happen by getting yourself into the wrong place at the wrong time, though that, at least for me, has been pretty minimal.
The Wii U version is currently having one disastrous glitch thanks to the day one patch. It wasn't an oversight because it didn't affect the EU owners, but for whatever season, it's affecting the US version. Basically, it removes the checkpoints in certain challenges, making the challenge themselves literally unbeatable. Sumo/S0L said they got a patch to fix this up, but it's not hosted online just yet.
2. Ryo's not in the game in playable form. The poll isn't meant to be a surefire confirmation that we will get DLC, it was just S0L challenging the fans to see if the requests are as strong as the fans say it is, and that the top 3 characters will be presented to SEGA. What SEGA decides to do and wether or not they decide to go ahead and let Sumo work on the DLC, we've yet to see.
3. Netcode is decent at best. Unfortunately, there are issues going on online where players with weak connections can bump other players out of the road with very little effort. There's also the issue of random disconnections every now and them. Sumo is apparently working on a patch for this as well.
http://backloggery.com/SetnaroX "Proper sound shatters glass. Proper sound shatters the Universe."