You have probably downloaded Games that not was created for Galaxy Tab.
Mobile version of Gameloft games will not look good on Tabs
Gameloft have a special category for Samsung Galaxy Tab that have games that works good on the bigger screen.
Use your Tab an go to www.Gameloft.com and they will detect that you have a Tab and will show you games that is made for the bigger screen and resolution.
Sent from my GT-P1000