The Gers were never at their best as Terry Butcher's men claimed a deserved 3-0 win at Ibrox to book their place in the last four.
After seeing off Motherwell in the last round, the Gers were strongly fancied to claim another SPL scalp and clinch a semi-final berth and McCulloch admits the Light Blue legions – who again turned out in huge numbers to back their side – deserved better as they slumped to a shock defeat.
"That was a disappointing night for us," he said.
"Inverness were the better team; they passed the ball better and created more chances. On the whole they probably deserved it more than us. There was something different tonight from the Motherwell game. The tempo wasn't there that we played at against Motherwell and that's disappointing. I don't know why that was.
"I think Inverness just wanted it more than us. Maybe this was just a bit of a reality check about how far we've got to go to get back to where we were. It will be a long road and will take some hard work to get there. We won't be getting carried away.
"We had 28,000 coming on a cold night and I think they deserved better than what we showed tonight. We didn't seem to get going."
Despite crashing out of another cup on home soil, there was good news for Rangers yesterday after McCulloch penned a new two-year deal with the club.
The skipper has been the standout performer for McCoist's side and he is keen to continue lead-ing by example and bring success back to Ibrox.
McCulloch said: "I am delighted to have signed another two years onto my contract. Hopefully in those two years we can get a bit of success and get back to where we belong."