ugg sorry about last night.... I felt like I was playing a decent Irelia, never fed in lane but we just couldn't win one and by the end I was way too drunk to do anything but stumble to bed. I'm not sure it's possible to miss a last hit as Irelia, but she is pretty mana intensive and that makes it somewhat hard to harass in lane.
Irelia is an odd champ in my opinion. AD assassin that does slightly less burst damage than xin with a little more innate survivability when not including xin's ult. This is because her Hiten style (W) a bit more consistent with life drain at later levels and for slightly more health. She is decent in a lane with her bladesurge (Q) to allow last hitting and still stay in the lane without being too mana intensive.
Her big problems for me are her Equilibrium Strike (E) and her ult (R). The E dashes forward to slow, like xin but with a faster cooldown, but doesn't do the same damage either. The E is a great for it's slowing ability, but only stuns if she has less % of health. If you are trying to run, this is hardly the best thing to do to get away as if you are lower and needing to get away then dashing back at your foes into melee range is very bad. Sure you stun them, but then you are in their grasp again. So to make use of the stun you need to be focused first, but have people on your team nearby to help out to capitalize upon a stun you did because you are low life. It's decent for chasing as an ability though since it does slow them down while bringing you into melee range, but the stun part is way too inconsistent. You CAN try to make it so that she is just slightly under 100% health before a team fight so that you can get a stun off on the enemy from the get go. But there is a chance that will bite you in the butt for not starting the fight at full if she is focused first.
Her R suffers as well from being 4 skill shots in a row. Sure they hit everything they pass through and the damage can be substantial if they all hit. However, it is very hard to line up multiple targets sometimes and then have all your targets stay in easy hitting range for all 4 of her ult attacks. Which means you rarely get to hit your target(s) with all 4 attacks of her ult. The less you hit the less damage her ult will do ultimately and can be significantly less damage.
She is a decent jungler, and decent in a lane, but I have never liked her as a character. She is similar to xin without having it true burst damage potential for slightly more survivability compared to when xin's ult is not up. Her CC is also very inconsistent and hard to capitalize upon unlike xin's knock up. Xin's isn't perfect since it is a delayed affect that requires three hits, but it always goes off on that third hit for a 1 second knockup which is like a 1 second stun.
Just never been a fan of irelia because of those shortcomings.