I find it interesting that my pumpkin ale recipe is still the #1 result on Google when someone searches just that ("pumpkin beer recipe" places me at #2). The recipe itself is an extract-based recipe (with partial mash elements), and I thought I’d relay some notes and thoughts on the brewing of it based on my experiences over the years. (This also helps me organize my thoughts a bit because I think I’m brewing up a batch of it this weekend.)
Gravity and alcohol content: I’ve noticed, depending on the big variable involved in the recipe (i.e., the pumpkin), that my original gravity readings tend to be way high for what I estimate they should be. This is mostly because of the pumpkin particulate present in the wort, and this will tend higher the mushier (or more pureed) the pumpkin is. I’ve gotten an ABV reading of over 8% before! A normal expectation for this recipe is in the neighborhood of 5 to 6 percent.
Spices: The recipe calls for adding the spices and vanilla right at the end of the boil, and that’s how I usually make the beer. The problem is, the primary fermentation can drive off a lot of the spice character from the finished beer (though I’ve always gotten a nice spice profile even so), so you might try adding the spices at different times. I added at bottling time once, and the beer tended toward being over-spiced, I thought. And once I tried adding the spices during the secondary fermentation to see if that balanced best, but I can’t speak to the results—that batch went bad.
I think if you’re going to stick with adding them at the end of the boil, bump them up to 1½ teaspoons.
Recipe variations: Instead of the Vienna malt, I’d just use American 2-row; it’s just the more efficient use of grain for a partial mash. (The original recipe was, I believe, adapted from one that appeared in Brew Your Own magazine eons ago, and at the time I had on hand a bunch of Vienna malt.) If you’re sticking with the "standard" type of pumpkin ale—basically an American Amber or Pale Ale—then I wouldn’t mess around with any other specialty grains. However, if you’re looking to mix it up a little and make a pumpkin stout or something (yum), go nuts.
Stroking my ego: If I do say so myself, this recipe makes a really good pumpkin beer—great aroma, solid flavors, and nice, chewy mouthfeel—really enjoyable. Something to look forward to. And, it’s easier than it sounds; you just need to put in some extra time handling the pumpkin. As Alton Brown says, your patience will be rewarded.