It was pretty much dry(when we saw it). I suppose if it were the first thing you saw, then it might impress you.
You will see a lot of elk in this area. You could also soak in the Boiling River area(near the entrance)

I suggest a full day or more at Upper Geyser Basin
See Old Faithful, Castle, Riverside, Daisy, Great Fountain, Beehive. Chances are you won't catch all of these, but I really like the first three.
A lot of people like to hike to Fairy Falls

See Fountain Paint Pots/Artist Paint Pots
Perhaps see Midway Geyser Basin.

You can spend the better part of a day driving thru Hayden and Lamar Valleys. Stop at Tower Falls.

You will want to spend 1/2 day or so at Canyon area most likely.

Might want to do a Lake tour and spend a little time there.

I wouldn't exclude Mammoth, but it would be the first thing I would cut if you are short on time. We stayed one night each at Roosevelt Lodge, Lake Hotel, Old Faithful Inn, and Colter Village Cabins in the Tetons. Really should have had one more night in Yellowstone.

Do consider driving Beartooth Hwy.

We usually do a lot of hiking in National Parks. This is one that we never had time to. There is that much to see and do right by the roads. I can only imagine that it must be just as awesome a couple of miles from the road. It is a very complete park--something for everyone. I don't really think you can go wrong any way you do it here really.

thank you for the advice....so far I plan to stay 2 nites at Colter village, 2 nites at Old Faithful cabins,1 nite at mammoth,and 2-3 nites at Canyon (or possibly a nite in Cody) not sure 100% but was thinking if we stayed in Mammoth it means less driving that nite....

I'd drop Old Faithful before I missed Mammoth!

I totally disagree with Sylvia about dropping Old Faithful over Mammoth.

I think you will have enough time to include Mammoth area on your trip though.

Have a great trip!!! sounds like you have it planned out nicely.

Old Faithful; reminds me of the Chevy Chase Vacation movie. Trials and travails to get to the Grand Canyon, and he looks ove the edge, says "uh huh, uh huh, back in the car!"
Seriously, visited the park for 40 years, even worked there, and the Old Faithful geyser can be quite underwhelming. However, it's a good location for visiting other geyser basins.

The first time you see it, Old Faithful is just fantastic. I've been to Yellowstone twice, and I cannot imagine going there and not seeing Old Faithful. Mammoth was fascinating too. It's not either/or, it's both.

If I get the chance to go again, Old Faithful is "must see" for me again. I know different strokes for different folks, but this one I would never understand

I think your plan is nicely laid out. I wouldn't omit either Mammoth or Old Faithful.

I spent 3 days in Mammoth a year ago this month, and found plenty to do there. The geyser basin was a beautiful walk for a few hours in the late afternoon when the sunlight was just perfect, and there are several park sponsored tours that you can take.

We saw all kinds of animals on a day long wildlife tour, including a pack of wolves, and a lone wolf who crossed the road right in front of out van! And there were bison right outside the Mammoth Lodge everyday, and elk on the hill right above the Lodge.

While Old Faithful itself might be underwhelming to some - it is hardly the only attraction in the area. I spent 3 days walking along the trails and boardwalks in the geyser basin. The area is spectacular and not to be missed.

thank you all! I do want to see both areas, but so many people on these forums seemed to not like mammoth very much...since I've never been there,it's hard to tell from pictures what is worth stopping for....Ok,so I'm going to continue as planned, because some of those ranger led tours sound very interesting! planning this is so exciting!

Good decision, hsmamato.

While I think it's helpful to get opinions from people, I don't think you should ever not do something you really want to do, just because some people say they didn't like it.

In fact, I had heard similar negative opinions about Mammoth before I went, but I really enjoyed it, so you should go and form your own opinion.

And BTW, the restaurant at Mammoth Lodge is excellent.

I think 1 night in mammoth would suffice. For me it' 2 nights at GTNP, 2 nights at old faithful area (access the lakes from here too), 1 night at the canyon area, 1 night at the roosevelt area, 1 night at mammoth. This is minimum. I would add nights if you have it.

In yellowstone lake, you can kayak and see a different perspective. Doing the thumb area walking then getting on a boat and paddling is seeing it from very different perspectives.

IN GTNP, we did an overnight kayak trip in grass island which was incredible. we did both paddling trips with oars.

i highly recommend doing the beartooth highway (from roosevelt/lamar valley area and even stay the night at red lodge montana - a very cool little town. make sure to visit the red lodge brewery from there. BTH is just absolutely a GORGEOUS drive!