My boyfriend returned the M8 for the Icon as he didn't really notice anything overall that was BETTER just different on the M8 and he missed the Nokia support and camera and all that good stuff..;...Some people on the comments from some articles do miss the Nokia apps and miss Nokia features and what not. While you may not be concerned with updates, it's still a good idea to be at least curious as to whether your OEM is going to get them out in a speedy time OR not.
From what the majority of M8 owners claim, it performs well and launches things faster than the Lumia(though the Lumia isn't laggy by any means and from using an M8, I didn't see much of a difference in speed) and the hardware is nice as well.
Most people here will tell you it is loads better than a Lumia, but in reality it really isn't. It's not WORSE than a Lumia, it's comparable.
To be impartial, if you really don't care about the camera(shock) or HTC questionable support and you like the phone, go for it. It is a good phone for those who might want something other than a Lumia. I'd much rather someone go to HTC, unfortunately, over leaving the platform entirely.
This video sums up the differences and similarities between the two phones(and negates the "M8 is faster because it has 801 vs the lumia on 800 processor" bs argument since the Professional reviewer himself says in certain cases, the M8 is faster and the icon is faster.)
Of course for me, I always recommend Lumia regardless. I am not bothered by the design(and I don't see it a slab really). Personally, I don't like the rounded edges of the M8. While both look like premium products, the Icon looks better to me with it's edges.
but yeah this video I watched yesterday really showcased that the Lumia Icon AND the M8 are nearly the same phone with a few key differences.
HTC One M8 for Windows vs Lumia Icon - YouTube