Ok so I finally got to seeing IW in the imax just a few days ago, now I can sleep easy knowing I no longer need to worry about spoilers thank fook.
Really enjoyed it overall and easily the best Avengers movie thus far, though to be fair that in itself doesn't really say much because they two previous ones were somewhat disappointing for me .... especially the 2nd.
The scale of IW was incredible and seeing it on the imax screen in 3D made for truly epic experience. The action was pretty much relentless and even at a fairly hefty 2 and a half hours really didn't ever feel like it was dragging.
Some of the scenes were truly awesome, Thanos vs Dr Strange the forging of Stormbreaker and of course the final battles among others. The cgi was top notch, when cgi first started to become widely used I never thought after some of the early crap that we would be seeing it used to such great effect with creatures, entire planets and galaxies so well rendered that they are virtually seamless. The star of the show, Thanos, was incredibly well done, although I still would have preferred him with White Walker-esque pale blue eyes and a bit more bass in his voice but hey ho we can't have it all can we

. I guess most importantly they gave us a villain with some real depth and feeling to him which was a real breath of fresh air compared to most of the weak bog standard baddies we've had thus far.
My main gripe with the movie was the humour, which after the more natural and genuinely felt humour of Ragnarok was back to the usual forced feel of the other MCU movies. Here in particular most of the gags fell flat for me and felt very out of place juxtiposed with the very serious tone and overall feeling of impending doom. I guess there weren't too many of these scenes or at least not enough to detract very much from what was otherwise an immensely enjoyable superhero extravaganza.
I rarely go to the cinema but this is the type of movie I like to catch on the big screen, one that is like a fully immersive thrill ride and though not quite perfect IW delivered the goods. A solid 8/10 from me.