I don't know, I think the Mass Effect series is still worth playing - taken as a whole it is still on par with TW3.
Yes - if you're a real RPG fan I highly, highly recommend that you take one single character through all 3 games on highest difficulty and all with all the DLC.
The DLC (lair of the shadow broker, arrival, leviathan, citadel etc etc) really help flesh out the universe and then the ending of Mass Effect 3 makes a lot more sense.
I took a single femshep infiltrator with the widow rifle through all 3 games and it was beyond epic. Saved Wrex, saved Eve, cured the genophage, united the geth and quarian, all team members survived the suicide mission etc etc...all the good stuff.
If you ONLY play Mass Effect 3 without and DLC I fully understand that the ending is a big WTF moment. But if you've gone through all the games and all the DLC there it's a completely different experience.