I have never had much luck with effects, I always end up leaving them off as they tend to cloud the mix and not add a nice ambiance.
On 80's style metal albums such as, Accepts "Balls to the wall" Judas Priest "Screaming for vengeance" I hear some ambiance or like "Room".
Every time I try to add reverbs or delays to distorted guitars, it always ends up a mess. I track in a very small room, it's well treated but lacks any sort of good room sound, with all the bass trapping and various treatment, the room is for the most part dead sounding.
Could somebody shed some light onto what I should be doing, proper use of reverbs, such as settings for pre-delays, room size, diffusions... It's all so complicated and the reverbs come with so many different settings it's downright confusing..
Were the above mentioned albums recorded in large rooms? Taking advantage of natural room reflections? This is what I would like to achieve, Natural sounding guitars and vocals, instead of obvious processed and fake sounding.
You can do what you describe using only reverb effects. The key is to have a very short decay time. Many reverbs come with presets named "Stage" and "Small Room" and so forth. That's what you want as a starting point.
It's also very important that your room be acoustically treated. Early reflections at the mix position make it very difficult to hear what you're doing while mixing. Once your room is treated properly you'll be able to discern small changes in reverb, level, panning, etc. Don't dismiss room treatment because it's the single most important thing you can do to help you create better mixes.
I'm not a big fan of reverb (of any kind) on Metal rhythmguitars, but nevertheless for an ambient drumsound I'd go for a IR reverb like Altiverb. Try to send the whole kit through the reverb, that's how I work.
I had great results with Virsyn Reflect as well.
For me, small room ambiance reverbs are the acid test of an artificial reverb. IMO, very few are capable of a good small room. Almost any reverb can do a reasonable hall effect, but many just sound bad for small room sounds.
ITB, this is where I think convolution impulses of real acoustic spaces work best. Even then, you might need to shrink them to get the tail short enough. And play with pre-delay, because that's the first big clue as to how far away the virtual walls are.
Capturing your room with a mic is worth playing with, because it's almost always going to sound more convincing. The idea of introducing plywood reflective panels is a good one, because you can have some control over the end result. You might even want to try a boundry mic or two on plywood panels.
The idea of boundry mics is to maximimise the room sound by plaing the mic right at a boundary. If you imagine an omni mic in free space, you can imagine that a lot of the waves either side of the mic will be effectively cancelling out the waves on the other side. By removing one side, you get less cancellation therefore a stronger room signal. You are also practically removing one room node, and in a small problem room, that can be a good thing. Hard to say without trying.
Many other mic options are worth exploring - trying whatever you already have for a start.
I agree that ambience is tough on heavy guitars. I generally try to use a very small amount of reverb on them. I don't remember exactgy which song (or songs) but I remember on And Justice For All there are some tracks with very slight reverbs on them, and I always thought it sounded good. Maybe even a short delay would add a little sense of space without losing the guitar's presence - just an idea.
Believe it or not, the 'Room' module from IK's CSR sounds really, really good. VERY tweakable (including the ability to EQ the reverb, incl. hi-cut/lo-cut). I am typically not a fan of reverb plug-ins. Aside from the UAD plate and some of the CSR stuff, I prefer even 'cheap' outboards to plugins. But, last night I was mixing an acoustic piece and the guitars (4 tracks) were all cut in my small, heavily 'deadened' ISO booth. They really needed some life. I set up a send, put the IK CSR Room reverb on it, spent about 10 or 12 minutes tweaking it and I was shocked at how real it sounded. Even in headphones at high and low volumes, if I hadn't know I was using a plugin, I'm not sure I would be able to tell that those guitars were not tracked in a medium sized room with great ambience!
I don't know if IK has a demo or not, but I would highly recommend it. It is worth the price, IMO for the 'Room' module alone.