as Jim said, no, its not bad, but it is different and requires a very different setup which usually keeps away the average person only needing to weld aluminum very seldom.

the alum. wire is softer and doesn't like to be fed long distances through typical MIG guns w/o birdnesting... which is why a special spool gun is generally required (generally a few hundred bucks and requiring a compatable machine).

for those using a 75/25 shielding gas setup, aluminum requies 100% argon meaning changing out tanks.

alumn doesn't conduct electricity as well meaning its going to require more from your machine (usually requiring the bigger 220v machines).

also, good prep/cleaning work is cricual to remove oxidation that occurs on the alum before welding.

-Rob