Hmm, usually most really good glitch-less levels appear in a pack amidst some other glitchy levels...
Some of the lesser-known good level packs that aren't ages old (here meaning older than about 5 years) that I at least don't remember in particular for having glitchy levels are SgB01/Fleech01, the ones by pieuw, by siergiej, Yawg06 and if I remember correctly, I think BulletRide's packs didn't make much use of glitches either, but I'm not quite as sure about that.
Oh and of course Insane Steve's latest one, ISteve10.
In any case, I found these levels pretty enjoyable, on a medium to hard difficulty scale, and not glitchy in particular.
And if you want a challenge, try tseug01/1tseug level 6.