The total dearth of HL2 mods is disappointing. Makes me sick to see as many empty CS:S servers as all other non-Valve HL2 mod servers combined.
PVKII and SourceForts are usually the only mods I notice as having a consistently decent number of players. SourceForts, however, is rife with elitists, so it's no wonder newbie penetration is so low. PVKII _looks_ very promising, but if they let people get too used to playing any one version, they'll suffer attrition that they can't afford.
As for ES: it's effectively dead. The first version was somewhat fun but extraordinarily buggy. The concept seems good, but some elements were poorly thought out (the big ion cannon was only any use _just_ as ships were landing, and then you were only able to kill the ones that couldn't land in a reasonable amount of time). I do applaud their efforts to bring some of the Battlefront 2 style of space combat to the Source engine--that was a great game that was, as is so familiar a tale, killed by Lucasarts' complete lack of support.