I personally found helix extremely overrated and actually a bit boring compared to modern launch coasters (notably Intamin; Taron, taiga etc). I enjoy icon because I think it's really the best of a bad bunch in the UK, it has a pretty weak layout but small pops of airtime and hang time make for a fun ride if you sit at the back. So yeah, whilst I find both helix and icon fun, I think icon is more of a novelty because its in the UK where we don't really have anything like it, whereas Helix is out in Europe with the big players and doesn't really compare IMO to other coasters out there in Europe.
To be honest I wasn't the biggest fan of the park either as a whole(the best thing about it is the chocolate tombolas everywhere!). I much preferred the atmosphere at Grona Lund, Grona Lund felt much more quirky and vibrant whereas Liseberg just felt a bit dead in terms of atmosphere.... I much preferred my second day at Liseberg to my first though as spent pretty much the whole of the first day queueing whereas on the second day I could appreciate the beauty of the gardens and detail within the park (really wanted to ride the big wheel but queue was too long and operations were also slow which was another gripe).
My other main issue with Liseberg was they advertised a closing time but the actual ride queue lines didn't have a particular closing time, they just seemed to close whenever the staff felt like it, so wanted to do a night ride on Helix but missed out because the queue line was shut way before park close...