Thanks to all for your input, experiences and some witty and very true comments.
"Always skip the 1st gen" and "wait, there's a fix and upgrade in, what looks like, 2032 !" are of course the expected comments. I for one have the 1st gen MacBook Pro Retina, and could not be more happy with it. Don't expect a product to be 100% perfect - there is no such thing. Lot's of "issues" addressed are often related to software bugs, be it Yosemite or let alone third party software still not adopted to the massive 5K screen and it's resolution(s). For me it's a flash-back to when I bought my riMBP 1st gen. No regrets whatsoever.
Yes, it's a massive investment for most people, pulling the tricker on a base or fully loaded iMac 5K, and people expect absolute flawless and instant miracles. It's a brand-new technology having a 5K screen, and if you want it today, buy it today but dont moan about what it would be like in 5 years from now. Wait 5 years. That's the dilemma or fact with being an "early adaptor" with any new technology.
If you want to play games, buy/build a PC or get a console. The iMac is not built for gamers for but a general purpose as an "all-in-one", as someone rightfully said here. It's a 2K worth screen where you happen to get a slick and fast computer for an extra 400 USD for the base model. Add what you want and can afford and don't complain about it.
I personally can't relate to people unboxing their brand new 5K and the first some apparently do, is immediately start to benchmark everything possible, throw every third-party software on it to measure temps of CPU and GPU and push their new machine to the absolute limits and beyond. Why can't people just don't enjoy it..? Yes, there is always a faulty product here and there with anything, but especially Apple is more than well known for how they handle those things.
Why is it so hard to actually share good experiences with a product? People want to get excited about their new-born iMac, and if some have made a wrong choice, don't yell it from the rooftop but swallow your pride.
Again, thanks to all of you for your input. I'm pushing that "BUY NOW" button for sure, adding a few things, wait.. don't sleep for the time the delivery takes.. laugh hysterically for no apparent reason other than the expectations for when the UPS guy is at my door and I unbox - and enjoy. It's actually a lot more fun to.. enjoy.