Well according to BJCP style guidelines, the IBU range should be 30 to 50.    I tend to like my ESB's on the higher side and a bit hoppy to balance the sweetness.    Your grain bill and yeast look about right.    What did you use for hops, East Kent Goldings, Fuggle, or Challenger?    If executed well it looks like a winner to me!

I hope to do one. It will probably be Palmer's recipe.

If my local brew store has Maris Otter grains, that is what I will buy.  I have seen the Maris Otter extract there.

Well done!

I just brewed an ESB yesterday using this recipe:

http://www.theelectricbrewery.com/forum/viewtopic.php?t=25410&postdays=0&postorder=asc&&start=0

Its a beautiful copper color, can't wait to give it a taste, the Wyeast 1968 is really going to town.  I did add a little more maris otter to the mash, and my pre-boil OG was 1.055 so I used another 1/2 ounce of challenger hops at 60 minutes to up the IBUs to about 40.  My OG going into the fermeter was 1.067.  I mashed at 149 because the british ale yeasts typically don't have a high attenuation and the more fermentable wort will allow for better attenuation before the yeast drops out.

I love to brew ESBs but I haven't brewed the above recipe yet.  Looked too good not give it a try.