I recently tried the single player of this game, and I liked it very much. I'm contemplating buying a copy and giving multiplayer a shot, how many players are there on the euro servers nowadays?

hardly any

I bought DM this weekend, and while enjoying the sp campaign (it's good, even great at times), I also tried mp.
Found 2 crowded servers, and most of the rest with pings over 200ms.

Actually, the European servers have more activity than the North American servers. We have one server that sees activity, while there are at least three or four European servers that stay fairly active. Looks terrible if you're coming from a really populated game, I'm sure.

The population has been getting a little better as of late, with the deal that Ubi was offering. Still, it's a dying game, so enjoy the mp while you can.