I like Source more. The original has more maps, but Source has better graphics, machineguns that can deploy anywhere (it makes a huge difference), those grenade-rifles (are those in the original? I can't even remember) and a few new maps. If you're a big fan of the first one, like I am, Source is definitely worth a buy. It might not be a replacement because of the lack of maps, but on the maps they have so far, it's more fun. IMHO.
there is something that makes the original Dod stand out from DodS and i dont quiet no what it is.... but i "feel" more like im there.... the sounds seem better..... or something. The Atmospher seems real...i dunno
either way ive stoped playing both due to lack of time and interest