I was thinking of rebuying this game too.
The MP is SO awesome.
Having any issues filling rooms?
Only when I didn't have the DLC.
I would end up in rooms with nobody.
There is still the occasional time the game launches and you end up with 1vs 4 but it fills up in less than a minute usually.
I did notice that nobody plays the "everybody capture the one node" mode anymore.
Tried launching that one 4 times now and I just end up alone in a lobby.
TDM and Conquest work just fine.