I beat number three and is it still worth playing the other ones or should I wait until the next trilogy is begun in 2016

I'm not the biggest fan of ME1, but it's definitely worth playing. ME2 is really great, but in different ways than 3. I played like you (first game I played was 3, then 2, then did a 1-3 playthrough), and while going back is difficult, you'll be shocked how much better the whole series gets when you play through all of it. You'll get way more attached to all the characters an get a lot more involved in the lore and events, and it's just a much more rewarding and fulfilling experience.

If you thought three was the apex of the series, then I feel sad for you. The answer is obviously yes. One was great, and two was a damn near perfect game. Play them, for the love of god, just play them!

A quick note, if you do play one, DON'T DO THE KEEPER QUEST WHATEVER YOU DO YOU'LL GO MAD FINDING TRYING TO FIND ALL OF THEM. But you know other than that I had fun with it, the mako is great for climbing mountains.
As for playing 2? I think 2 has the best build up of any of them, I actually just finished playing it the other day and the suicide mission still made me nervous. This is coming from someone who has beaten it probably ten times, and it still makes me nervous picking my specialists and squad leaders, even with that flowchart I still am afraid that someone will die.

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You played number three without playing the rest of the series? What in the world is wrong with you? Since it's a single, unified series, you've missed out on the build up to most if not all of the third game, plus you don't know any of the context of your actions or your position in the universe. It's the game equivalent of watching Return of the Jedi without seeing any other Star Wars movies beforehand... and without watching them afterwards, either!