I'd give this season a 4.
It was enjoyable and I looked forward to seeing the next episode. The action sequences were very good, especially the climax of "Remember it" (that tri-headed sentinel needs to show up in the MCU X-Men for a good dose of horror). Most of the characters were likeable, and it definitely improved Cyclops and Jean from the original animated series.
My main complaint of the series would be Rogue and the love triangle. Although the character improved in the last few episodes, those first few episodes and her cheating on Gambit made her my least liked character in the series, which is a shame as she was my favourite character in the original series. Also I think they could do with replacing the voice actress because the voice sounds old and a bit damaged whereas Storm's voice actress still suits the character.
I think having the characters change their costumes is a good idea (and is hopefully reflected in the opening credits next season) as it helps to begin to separate it from the original series.