Which, Mr. Beer, beer style/Hopped Malt Extract was it that you used? Did you only use one 1.2lb can of HME or more? Can't be absolutely sure but it sounds like maybe you didn't have a pack of booster either.
Probably would be best to leave this present brew to age for a decent while, a good couple of months, and have a look on the Mr. Beer web site to check out what's available and appealing to your tastes. There are 4 levels of ingredient kit (Refills) you can choose from for beer. Standard, deluxe, premium and seasonals.
Many people reckon the standards lack any real flavour and depth being one can HME and a pack of booster, deluxe being fuller bodied, flavourful and maltier due to using one can each of the HME and Unhopped Malt Extracts as an additional fermentable. Premiums are better yet using two cans of HME and the seasonals are the equivalent malt addition as three cans HME/UME (3.6lbs). You can also buy everything available as individual ingredients, if you so wish. HMEs, UMEs, hops
Don't know if you like the style but if you do like an IPA I'd highly recommend the American Devil IPA kit. This was my 2nd attempt at homebrewing and it came out really, surprisingly, well. Made a couple of additions to boost ABV and flavour a bit.
Two cans American Devil IPA HME. 500grs (1.1lb) coopers light Liquid Malt Extract, 1/2 pack of Mr. Beer booster. 1 pack safale S-04 yeast (and also chucked in the 2 little packets of Mr. Beer dry ale yeast, too) Fermented in the keg for 3 weeks, bottle conditioned for over a month now and it's unbelievably good. Really nice balance between malty, sweet and round followed by a nice hoppy afterglow with a really pleasant aroma
If you have a lhbs nearby you will probably find that larger cans of HMEs, UMEs and various other ingredients will work out cheaper than the MR. B stuff.
Best of luck with your brewing and welcome to the addiction.