I am of the opinion that paintball-specific gear -- the right kinds, and the right way -- is one of the best investments you can make in the sport.
Paintball specific pants are at the front of my list. A good pair has many features over BDU or hunting-type pants, including lightweight materials (nylon), breathable mesh, stretch panels, paintball-specific pockets (e.g. swab pockets), and integral padding. The pants help you stay cooler and move more freely, which is key and is not as much of a priority with, say, hunting pants, where very fast movement/running is simply not part of the design consideration. Good pairs are also very durable and can take sliding, abrasion, etc. for years. A controversial aspect of pants is the oversize design and integral padding, which leads to bounces, but that does keep you in games. Some pants even have padded zipper areas
Jerseys are a tossup, but I like them with the right features. First is breathable sport materials and/or mesh, for keeping cool (I play in the tropics). I like jerseys with integral forearm/elbow padding for crawling. You can find some nice camo jerseys these days since camo is trendy, plus some scenario companies are stepping up.
Paintball specific gloves are a decent investment as well. The materials you find in them are not common in other applications -- thin palms for shooting and marker handling, lightweight/breathable/sport-type materials on the backs for flexibility, speed and padding. If you can find these features in other gloves then those would be fine too.
Paintball specific pads are a fairly good investment, though these are probably an area where many other sports' equipment can be adapted. That said, paintball pads tend to have purposeful design, such as "enough but not too much" protection, i.e. no hard shells, minimal bulk, all of which can make a difference at the edges in certain situations. I personally like the dense gel-type kneepads that makers like Dye put out; I don't think this type is common in other sports.
Now when I say the 'right way' I basically mean, look for secondhand stuff. Because of the fashion show nature of the game (and kids' short attention spans), new or almost new clothing comes up secondhand all the time. Check especially on PBN. You can get last year's model of tourney pants in good condition for like 30-40 bucks. There is no excuse for not having decent gear at those prices.