What's the most obvious difference between human and engine play? With the weak or down-regulated engines I've seen (below 1000, but perhaps specially between 500 and 900) the only thing that striked me as odd was how they seemed to simply give away free queens or other pieces every now and then. Lower than that I think that the most obvious difference was the humans would tend to use the queen a bit more and make more moves with the same piece or pawn early on. But past 1000 (and I didn't go far beyond that, only something like 1200) I couldn't notice anything very weird, inhuman. Except on situations such as a engine vs engine match I saw on youtube, where when they're at a balanced position, they kept just moving the rooks and/or other pieces safely at random and useless positions. The narrator of the video called that an "staring contest", which I think that may have taken something like 30 turns.
Low level computers play pretty much perfectly for most of their moves, but a few times each game they make blunders that no human at their level would make, like giving away pieces.
I just realized how deep I could actually think and how fast I could do it. If you read my "VULPES_VULPES vs. Excalibur" forum series, you might discover my playing style there.
I literally do better when I think aloud and wave a pen around the square that I think of moving the pieces too.