Rogue is a funny class.
1 level of rogue unlocks all the skills you need to be a trapsmith.
2 levels of rogue give you evasion.
After that, the most important thing rogue levels give is sneak attack damage and unlocking assassin and acrobat enhancements.
My take: rogue splashes are for trapsmithing, rogues are for DPS with trapsmithing.
Keep in mind DDO (like D&D) is hugely flexible in character development. It's perfectly possible to create a nearly useless character if you try hard enough. No other game has the customization options (except maybe Asheron's Call), so you shouldn't try to pigeonhole class = role like you do with other games. I've seen melee wizards, I've seen trapsmith clerics, I've seen em all, and I think it's pure awesome.
A lot of people do come to this game from other games and say something like "I want to play a tank." But tanks don't work in DDO like they do in other games. Intimidate is a skill like any other, one level of splash to unlock it, then whatever other class levels to increase survivability. Or don't bother to splash and keep it at cross-class points, relying on equipment to get your score up high enough to be useful. And then once you've rolled up an intimitank, you'll find that some people completely ignore whatever useful things you are doing in their rush to zerg to the end.
I think that coming to this game from Asheron's Call like I do is one of the reasons I reroll so much.. I am enthralled by the nearly endless character and roll-ignoring possibilities.