Understand Plynkes argument but respectfully disagree. One can skirmish in any scale and 15 mm is a good one for it, smallest scale where individual figures stand out. The trick is doing skirmish on a very small table - it is a skirmish, after all. Or a very large skirmish with scads of figures can work, too. Having said all that, I'm personally not a big fan of skirmish gaming, even for my beloved French and Indian War - when done (getting closer) I'll have 28 companies with about 42 figures per company plus lots of gunners, casualties, civilians and native villagers (and, fitting with my bestial quirk, lots of animals).
Now, as to being impressed by a 15 mm or, in this case, 18 mm, my benchmark is Blue Moon's Sherlock Holmes figure (found in the Horror range) which is one of the best figures I've ever seen in any scale all the way up to 54 mm. It is a spectacular sculpt. Here is a link to group picture from the pack:
http://www.bluemoonmanufacturing.com/view_product.php?product=15HOR-114. I know it is hard to see in such small size as a group shot but it is truly lovely work.