 If you liked
Noein: Mou Hitori no Kimi e
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 ...then you might like
Dual! Parallel Lun-Lun Monogatari
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If you like stories about parallel worlds/realities like the ones in Noein, so you must try Dual! too.
We can't compare the two storylines at all because Dual! is a comedy series, but it's highly recommended to relax a little after the intensity of Noein. A good point in my opinion are the mechas on Dual!, they're cool!
In short, both animes have the same theme (parallel realities), but with a totally different development and outcome.