I played the stock game about halfway through and enjoyed it alot. I went right from SH2 to 5 so I of course thought it was a huge improvement, but as I learned later, there was much disappointment in what was left out after 3 and 4. Not to mention the bugs. I've only experienced the CO2 bug but I've read that there are others. That said, I'm now running mods and they've made it MUCH more enjoyable. I had planned to play it stock all the way through while learning how to use mods. This is the first game I've used mods on and I had lots to learn. Once I had a grasp on how to install and activate the mods I decided to just give it a go. I had a little trouble at first with putting stuff in the right place, but once a few of the members here explained some things I had it working. IMO it's not bad stock but I also didn't have the highest standards I would have had I come straight from SH4.
Hope that helps
