Twin Peaks is the kind of series you'll either love or hate. Unfortunately there's no way of telling which camp you'll be in until you actually watch an episode! It doesn't seem to have a specific audience that it appeals to.
But if you do go for it, don't watch the film until after the series as it gives away the killer!

Edit: a few more notes, if you like David Lynch films you'll almost certainly enjoy the first series as that is very Lynch. The second series comes across as Lynch-lite as Mark Frost seems to have a lot more influence in this one. That's not a bad thing as you tend to get less headaches watching these episodes! And it's not to say that series 2 plays safe - it contains some of the most disturbing scenes shown in a TV series!

Nowhere man was a decent series.  It was a conspiracy-type story where the main character couldn't trust anyone anymore, wandering around much like the old Incredible Hulk/Fugitive series.  The only problem was that it never really ended satisfactorily.  They saw the impending cancellation and answered a lot of questions, but you just know that given the proper time to tell the story the way they wanted would have been far more preferable.  Still worth a watch though, if you enjoy that kind of story.  It was quite well done.

Given the type of series you're asking about, Pete, I was just about to recommend American Gothic, but I see it's already in your collection. 

Northbloke is right... if you can appreciate Lynch even a little the first season of Twin Peaks is terrific. Funny and weird.  Season Two was uneven but with some amazing (and disturbing) moments.

The movie, if watched at all, should be watched last.  It answered questions that didn't need answered.  It's only really needed if you are a completest.

twin peaks without a shadow of a doubt

Actually, another reason I mentioned American Gothic is the way the end was handled.  Impending cancellation, they tried to answer as many questions as they could with the time they had left.  Nowhere Man does the same type of thing at the end of the series.

Thanks for all the replies... sounds like I will probably be buying both these series the next time I place an order. 

Quoting Addicted2DVD:

Quote:
and researched to find out what turns out to be a movie prequil (Fire Walk With Me) is not included in this set (so how is it the Definitive collection!?!?).. so I would be buying this movie separately at the same time... which means I need to ask... should I watch "Fire Walk With Me" first... or save it till the end as it would spoil the series for me?[/i][/b]

Thanks in advance for any and all help!

It's a definitive series as it includes the Pilot episode and therefore starts the 29 episodes off to a Bang start.. The definitive series does not include the Fire Walk With Me., and as well it shouldn't.
But do try and track down and watch After you have spent the better part of a month or a week (if you can do it)  and watch the whole set with a good Pot of Coffee and Lots of Cherry Pie..