It's nice to see some different opinions on here!
I personally think Darren's acting is really good, and I think he grew into his role. I wasn't impressed at all in episodes like Never Been Kissed or Silly Love Songs, but ever since Original Song I think his acting has improved dramatically (except during Blackbird, that was some creepy staring!). I especially love how well he handled Prom Queen - it was his first opportunity to give Blaine some kind of back story, and I think he nailed it. As for The Purple Piano Project: I was actually struck by how good his acting was, especially when he was announcing his transfer.
About the chemistry between Chris Colfer and Darren Criss: to me, they are the best on-screen couple I have ever seen. The way they just
beam at each other is incredible. It's like they just can't stop smiling when they're together!
Am I blinded by my love for Darren and Chris? Maybe.
But in all seriousness, I really do think they both are very good actors. Chris is better than Darren, but then again, Chris is better than practically everybody so that's not a fair comparison.
Just my opinion, of course. Like I said it's nice to see people disagree for a change. I live in such a Klaine fangirl bubble that I sometimes forget that there are people out there with different opinions