I've bought a Helix LT and am quite happy with it. Great unit, but for me it's lacking some essential effects.
First, I was surprised there is no boost pedal to be found in the Helix. I previously owned a Kemper powerrack and a boost pedal
has become an essential part for me when building a sound. So I'm wishing for a few great boost pedals.
To name a few: MXR micro amp, Xotic EP booster or AC booster.
Second, I have a hard time finding a great drive pedal in the collection. Especially the fuzz pedals I find particularly useless, whereas an original Fuzzface (i.e.) can sound awesome. On the Helix all definition is lost and even with the fuzz/gain turned all the way down. On other moddeling units they sounded more natural and definitely more usable.
So, in addition to an overhaul of the stock fuzz pedals, I would very much like one or two drive pedals that sound great, like the Xotic BB preamp or Fulltone Fulldrive. So far the only distortions I use are the Timmy, Klon and TS models. The others are not and have never been my cup of tea (RAT for example).
As far as the other effects, so far I am pretty happy. Love the fact that I can use IRs, but find that 128 memory slots proved to be not enough when sorting out my IRs. That's become a long tedious proces of loading, sorting/playing and deleting. And repeat. Still, love that I can use IRs to sculp my sound to my own taste.