If you're a fan of Morrowind then I'd say you already have a pretty good idea of what to expect from Oblivion. If you like one, I think the chances are pretty good that you may like the other.
As far as being "grindy" goes, I think that Oblivion is less grindy than Morrowind was. Morrowind was more static and sometimes (especially in the early levels when we are still in Seyda Neen) it could be a good idea to grind up a bit before heading out to Balmora or some other place.
Oblivion is not like that. The game world levels up pretty closely with you most of the time, preventing the need for "Seyda Neen grinding" syndrome. You can find a pretty good challenge wherever you go, at most any level. In fact I'd say that Oblivion is perhaps the least grindy game in the whole Elder Scrolls series.
There is a great deal of lore in the game, as there was in Morrowind. People will disagree about whether it adequately represented the lore of earlier games. But I think the lore in this game is fine. I think the lore in Morrowind is probably a bit deeper and more interesting than the lore found in Oblivion, but I don't think there is anything fundamentally wrong with the lore in this game. Some people may even prefer the lore in this game over the lore in the other games. It all comes down to personal taste.
So if you are mostly worried about grinding and lore, I don't think you need to worry. This is a great game, as Morrowind was. It is well worth all of the time and attention you put into playing it. I heartily recommend Oblivion to you.