I've had an Expert 45 for a while now. I haven't tried the longslide Glocks, but I have shot a 17, 19, 23 and 21 ALOT.
To me, the Glocks are fine guns. Simple, accurate, durable and very very reliable.
The Expert is just a lot more refined; controls (safety & slide release where they belong), a nicer trigger IMHO and a much better feel. For me, the Expert also points better making follow up shots quicker.