Sorry, haven't played this trough due to my other activities, but I'll give you some of my opinions & experiences. I was not going to test this at all, since you described it a long and hard mission...
First of all, I experienced no lag whatsoever. But actually, I've not yet been in any large battles. OFP Benchmark is 6880, no ecp.
Didn't like the overview, it really was a bit confusing.
Intro was quite nice, I'm no expert in these things, but yeah, some camera angles weren't absolutely perfect. Also, I didn't like the background story. It was maybe good, but I didn't like it. But it's just me, don't change it.
Actually, I didn't like the 'storyline' either, but that's just because I'm not fan of that kind of stories. USA would never leave it's soldiers on some small isle, even if a war had to be kept in secret. ;D But I think many people will like that story, don't change it, it's just me.
Briefing had only one problem - I didn't exactly know what there was in the village except my uncle.
The start was boring. Yeah. For the beginning it was nice feeling of walking in the rain uphill, but it's a bit too long walk - or I'm just impatient.
But let's say, at this point I noticed that time acceleration was not allowed.
In the village I went to the house where the fire was burning. The soldier first just watched me, so I thought he wasn't hostile. I went on to the other side, but at this point they started shooting at me. I was surprised and wounded, but killed them with my pistol.
Then I explored a bit the village. Didn't find anything special, no sign of my uncle, who had solutions for every problem I had. Yeah.
I got back to the house where I killed the soldiers, and noticed Tatyana in the back room. Cutscene.
Then, I killed the soldier who had shot my cousin. Took a jeep and started looking at my map. Oh, there it is. Off I went. Some soldiers were by the road, they didn't care about a jeep passing by, which was good. I've always wondered how can soldiers see from 100 meters that the driver of the vehicle is an enemy....
I took a bad turn and drove wrong way. Noticed it and got back to the right road. A convoy passed by me. That was nice.
Went off-road and to the cottage. No uncle, but Tatyana's husband. Unca's killed. Oh yes. Let's kill them all together - how sweet. There was a brief pause between two cutscenes and I think they'd been better as one cutscene. (Nice objective you've got there between them; Find your uncle. Kill them all!!!)
Okay, at this point, I saved and quit. Don't know anything about the remaining mission, but killing them all seems a good challenge, since this is one single mission, not a campaign...
Getting back to it later, perhaps.