Personally, if it's your first time playing PoE1, I would recommend playing the original campaign and after it adding the expansion. It's true that WM doesn't impact directly the campaign, but the experience of surviving Endless Path and your lvl progression changes forever once you have the expansion. Also, the dynamic of the soulbound items also changes the strategies of what to visit first.
Thank you for your input.
This is why I asked the question. For example, Baldur's Gate 1 provides a different experience without the expansion. True, the new areas are separate, but the extra XP and items you get from them, makes the orginal campaign different in some ways.
Baldur's Gate 2 on the other hand doesn't suffer from it. If you leave the expansion area that's accesible in the original campaign till after your finish (and skip the Wild Mage, something you should do on your first run anyway), then your original campaign experience remains more or less same. True you might get a High Level Ability while still in the original campaign, but it's not something that will matter all that much.
Eh, I really miss playing vanilla Icewind Dale. Exploring the Dragon's Eye and Severed Hand without War Chant of Sith is something different... to se ne vrati.
I'm torn. I'm really tempted to listen to your advice to get the original experience; especially with the people above mentioning the difficulty curve getting a bit out of whack with the expansions.
I don't want to risk havig to trudge through the original campaign again, just to try the expansions.
So, my quesiton is: is the game replayable?
Without making assumptions for how much the game is liked.
For example: Despite loving Might and Magic 6, a lot more than I liked Diablo, I'd call the latter more replayable: playing a Mage/Fighter gives different experiences as well as getting different quests. Might and Magic 6 on the other hand, despite having different classes, can be experienced "wholly" by having a balanced party and a balanced mix of skills.
How is PoE in that regard?