I didn't like to bring this up while the jam was running, but please don't spam other devs' games begging people to play your own. Especially don't beg for "really GOOD" ratings: in a lot of jams there are rules against telling people how to vote so it's likely to get you disqualified.
I appreciate that it's hard to organise people to have a go at multiplayer games in particular, but this kind of thing is going to put them off more than it's going to help. Try offering a time you'll be online to play against every day. Try getting in touch with other developers who've entered multiplayer games and asking politely - once - if you can find a time to play each other's games together so there's a chance to rate them. Make it easy for people to have a go, don't just post "plzzzzzzzzzz" everywhere you can think of.