Would my comment count here? S4 i9500 was my 30th phone, well if that gives me any credibility. I used it for a good eight and a half months.
Now about your queries,
CM compatibility? No idea! I personally dislike CM and have absolutely no idea about it. But you can visit XDA anyway.
How is the camera? Well it's damn good, that's how I want to put it. Now I have no idea if some new phones popping out nowadays have better camera or not, but again, you can go to GSMA and check the samples. But DO NOT expect great low light images (talking about Xperia Z3 etc. here) but the HDR mode does the job just fine.
Heating issue? What the heck is that? Some people expect an Octa core phone to run cool in our ambient when you do CPU/GPU intensive tasks?
Anyway, no, I didn't have any heating issues, at least those were not issues in my dictionary. Yes, the earpiece would get a little hot if you talk for more than half an hour, but which phone is there which acts differently? At least I haven't had any such model!
About your final query, no idea, and I can't and won't compare Apples with Oranges.
Take a note though, I was extremely angry with the phone after using it for eight months, because I was starting to hate TouchWiz. The main problem was with the TouchWiz stock lockscreen, the time there would not update with the system time, it would stuck at an earlier time and that lead to me to miss office at least three days. That was my main reason to sell the phone, and amongst other reasons there was the lack of support from XDA devs, especially for the Exynos model. I am not talking about a custom ROM or kernel here, but those flashable zips which fix a lot of problems (for me it was the flashable zip which would fix the broken screen mirroring which was caused for using a custom kernel). Overall TouchWiz was becoming unbearable for me, I simple hated that, period.
So then I bought the Moto X, then HTC M7 and after having
brilliant experiences with them I am now back with Note 3, and get this straight, I am not moving to anything else, at least not in the next one to two year period. Be assured, whatever you get, you will make compromises either here or there. I just made which was less in number, that's all.
Now I don't know what type of user you are, but if you are one of those heavy users (aka Power users) then I suggest you to get the Snapdragon model (no, not because the chip is better, because of dev support) over Exynos model, but in that you will lose warranty, if that matters to you. If you don't care about warranty then you can also get the GPE of the S4, well if you could find them anywhere.
Oh by the way, if I have read right it has already got the official Lollipop update, and I can assure you its a great update. I mean those micro-stuttering which were there present on TW version of KK, is almost gone from LP version of TW. Well maybe due to the runtime change, but I don't know. That lockscreen clock issue has also been sorted out, if you care about that.
To put it simply, yes, S4 at 18k is more than worth it. You will get a gorgeous display, a good enough camera, a phone with compact size, and the points which no one will tell you, a phone with great SAR value (it matters to me), very good call quality, a LED notifier, a camera lens glass which you needn't to worry about getting scratched in whatever way you use it etc., what you won't get, a near stock Android experience, a great build quality (talking about HTCs here, nothing else).
Anything else?