The Elantra's 2.0 Liter DOHC Inline 4 produces 138 horsepower and 136 foot lbs or torque. This is more than enough for a car that only weighs about 2600 lbs. In fact, it's actually quite powerful for a 4 cylinder. It only has 2 horsepower less than a Civic, however it has 8 more foot lbs of torque.
My Elantra has plenty of pick-up. I do almost all highway driving, and I find it very comfortable on the highway. the steering is very vague, and it gives you almost no road feel, however, I got used to it very quickly. I have no problems driving through city traffic (don't do it often, but haven't found any problems with it when I have) and merging onto the highway is a breeze.
I would chalk up your complaints to the fact that your Elantra has an automatic transmission. I have a 5 speed manual. In a small economy car, that doesn't make a ton of power, a manual just makes more sense because it can get more power to the wheels than an automatic. Now I'm not saying everyone should buy a manual car, I'm aware of the fact that there are people who physically cannot drive one (a good friend of mine has leg problems that prevent her from driving a manual), I'm just saying that a manual transmission will provide better fuel economy and improved acceleration when compared to the same car equipped with an automatic transmission.
Any car, Hyundai or not, with a 4 banger will feel underpowered compared to a V6.
I agree about the auto tranny. I just spent three weeks driving an Elantra 4,500 miles around the western United States. It would have been a good, comfortable car for long distance cruising, except for that dreadful auto tranny! The whole time I kept thinking how much better it would be with a manual transmission. The auto was so indecisive and really didn't know how to deal with any sort of incline at high speeds, especially with the cruise control on.
Other than that and the rather numb steering, it was a great little car, especially around town, where it proved to be very nimble, quick (from a standing start) and fuel frugal.