Why do jets from FS2000 fly like bricks with wings

ive only had this game for a week, thanks to my uncle, and I wanted to fly some more modern jets. I downloaded a few after reading that they could be incorporated into CFS2. Am I missing something?
Flight Simulator and other chat
https://forums.simviation.com/phpBB3/
https://forums.simviation.com/phpBB3/viewtopic.php?f=5&t=18482
. I dont have a joystick, and use a mouse, but i've always had great success with most planes before. I just need to figure out what hindrance is on my jets and solve the problem. Help!