I’ve been playing quite a lot of Mario Kart DS online of late which is excellent fun on the whole.
Good things: It’s super-easy to connect and a find a race. It all seems to work and hang together very well - I’ve had no errors or disconnections or anything.
Bad things: You can’t choose who to race against or even see who they are before racing them. You can’t swap friend codes with people who you randomly end up racing.