Yeah, Equal Rites is one of my least favorites - Color of Magic and Light Fantastic aren't as bad, if you can be persuaded to give then a go. The major characters, Rincewind, Twoflower, and Cohen in Fantastic aren't changed too much in recent books. In fact, the background on Cohen and Twoflower makes Interesting Times a little richer.
You may still end up separating them from canon, but they come across fine if you go in expecting a lighter story and less-developed Ankh-Morpork - an Ankh-Morpork pulled straight from Sword and Sorcery stock settings, that needs to be burnt down and rebuilt a couple of times before becoming the AM we all know and love, an Unseen University before Ridcully's stabilizing effect, etc.
The only thing you really need to dismiss is any personal details given about the Patrician, who really has not 'become' Vetinari yet. But aside from that, there's a lot of fun in them. The Light Fantastic was my favorite Discworld book for a long time.
Previously Catrine until my account crashed.