There is something not quite right with UFO Activity compared to the original.
Out of curiosity I started 10 games in Europe on a veteran difficulty level. In 9 of them I have detected no less than 3 UFOs in January, in some of them 5 or 6, and there was a guaranteed terror mission before the end of the month.
With OpenXcom I have 5 games where I only detect 1 UFO in January. In one of them it's April and I have detected only 3 UFOs total. Some of the games didn't have terror missions in January, though in these cases there was one somewhere in the early February.
Now, I get that these things are probably random and the graphs show UFO activity in other regions, but there is still a discrepancy between the original experience and OpenXcom, and not a good one. Now I can get positive scores without lifting a finger, and this never happened in the original. The negative scores you get for idleness are also lower (that is, you get better results) than they were in the original. Generally, I can see a 200-300 points difference in the first two months (say, -1100 vs -800 in January, and -100 vs +100 in February). Makes it harder to lose the game.
This leads me to believe that either aliens are far less active than they were, or something else is wrong.
I believe the point was raised in
this thread before.