70%
Originally, Robert Holmes had been commissioned to write the twentieth anniversary, but he found the challenge of writing a good story while juggling the number of Doctor Who regulars too daunting. The task therefore fell to Terrance Dicks. While it may not be the best story around, it manages to deliver an enjoyable tale with some wonderful moments. Superior to The Three Doctors, this story succeeds where that story failed. It maintained the spark between the various characters especially by keeping the Doctors apart until the end. Some characters were underused, although that was a common failing of the Saward era.
It is interesting to remember that this was the first feature length Doctor Who story, the first story broadcast in the USA before it was broadcast in the UK and the first and only time that a significant portion of the BBC telethon, Children In Need, was given over to one show. It probably wouldn't happen now but serves as a reminder of how popular the show was at the time. Perhaps this marked the last time the show enjoyed any real popularity? Although not one of the best stories this is a highly enjoyable adventure. Its one of the few stories of its type that actually works.
My understanding is that director Peter Moffat and producer John Nathan-Turner were not keen on the special edition: the version screen in 1983 was the finished product. While I disagree, I think the extended version has a slight edge on the original version, I also think that both versions should be available. As I have mentioned in my note about the extras, maybe BBC Worldwide will re-release The Five Doctors on DVD a la The Curse of Fenric - especially if they could include some extra features.