Some are excellent, others are not, and a lot has to do with the attitude you bring in.
Most of the actors are performing fairly tongue in cheek. The humor is usually ribald and crass (think Shakespearean innuendo). The beggars will usually do fairly disgusting things. There will often be pirates, gypsies, corrupt nobles and churchmen, etc. and scandals that need to be figured out.
Swordplay is in the Erol Flynn, swashbuckling style rather than authentic.
Jousting is di rigeur. It's usually fairly fun.
Be willing to put aside your personal inhibitions a bit and get into the crowd interaction.
Food is usually frighteningly expensive, as are drinks and souveniers.
Music will usually be along the lines of Elizabethan Madrigals or Irish and Scottish folk songs. This is almost always worth your time.
Many regular Faire goers will constume up and go in a persona. This can get REALLY expensive, as proper kit is generally handmade. A good sword (as opposed to a POS wallhanger that looks like a real sword) will run you 300 dollars to several thousand for a true work of art that is also as combat capable as any sword ever made. There are high quality, combat capable swords available for less, but they will also be less pretty. Angus Trim makes very good swords at affordable prices, but they are plain, workmanlike swords (much like what would actually have been used in war). If you have the spare change, you can buy an Angus Trim sword through Christian Fletcher and then have him spruce it up with custom hilts, pommels, grips, sheaths, etc. The prices of these lovely and functional aftermarket products is stunning, they'll easily double or triple the cost of the sword.
There are other makers who actually sell at the Faires, such as Starfire Swords. Starfire also sells a lot of the tournament swords. They are fine for make-believe, but they are generally WAAAY overweight and come with rebated points and edges (about a 1/16th flat on the edge and point to prevent actual cutting. ) Modifying a Starfire to lighten it to closer to real specs is an ordeal requiring a lot of grinding and re-heat treating. (Ask me how I know).
Just go and have fun. Don't worry about costumes or any of that (I got over bothering years and years ago...I keep swords for their original purpose only anymore, as a defensive weapon. )