Hmm... Sounds interesting!
-New misions every week - a lot of work, but can be easily done (without save'ing)
-alpha effects (fog) - GTA engine don't support it
Can be done from "outside" GTA II, but it will take a lot of GPU
-snow/rain - can be done, but without effects on ground (because you need 3 kinds of each textures - dry, wet and covered with snow)- Falling stuff can be made by script (needs a lot of memory!!!), or from some program working in backround (easiest way)
-Time change (day/night) Very easy to make with script - It was on Snowball City 2 (you are beggining at day, after one mission it becames darker, and darker)
-Clock - because it is not default GTA2 clock can be done from "outside" (like chat in MTA)
-Temperature - ????? With what kind of efffect? Changes in grip?
-missions/phones - easy stuff
-New multi - Why we need new if we got one improved with some game finders? And who will play with 1999 other players? Someone with 100Mbit internet connection?
-New weapons - sounds interesting - I DK how you will do this...
-Motorcycles - It CAN be done - with a lot of script (falling, lying bike, dissapearing ped on bike etc)
-talking to peds - it seems to be easy to done...
This is so much to do, so now it seems to be like unrealistic dream, but when it will be done it will be the best GTA mod EVER!
I can be a betatester - just because I want to know how all of this will be done
One thing - it will need a very good computer to run smoothly (because this weather effects, and a lot of script)
What about gun shops, like 3 of them on my unfinished map "oakland"? (www.mibars.prv.pl - gta2 section - bit old one, because i got some map editor problems)