I have the LS model and even with some frustrations.....overall it has been a very good car.
Like many other Impala owners, I've experienced several common issues.
catalytic converters wearing out, brakes, computers.
For cars made during these year models, GM still had not perfected their hubless brake rotors meaning....they dont dissipate heat well and tend to warp causing premature wear, shimmying on the steering wheel, etc.
Try installing high quality performance brake parts. I spent $250 on 2 new slotted & drilled front brake rotors plus high quality metallic pads. I quit having brake problems.
I like this car because of its value for the money.
No....this isn't a Mercedes or Infiniti but, for what I paid for it, it's a great value.
I need a car to one thing...get me from point-A to point-B.
But the impala does that with a very comfortable ride, mine has all power features, heated leather seats, good sound system, great visibility, great handling and engine performance.
I regularly get 22-23+ mpg around town with the AC on and I've experienced 30-32 mpg on long road trips....no complaints here.
And this is the 3.8L V6.
I've had mechanics tell me Impalas are great cars IF you take care of them and I had a body repairman tell me Impalas are some of the easiest cars to repair.
The problem with converters is caused primarily from the ethanol in the gas.
Ethanol breaks down too easily, tends to attract water and creates a lot of carbon when burned in combustion chambers.
A few solutions: Every 10-15 tanks of gas, use some high quality fuel treatment like, Lucas or RXP. This helps remove carbon buildup on engine parts and allows it to get blown out the exhaust.
Another good thing to do is when running the fuel treatment, is to do a few hard accelerations say...going down an access road.
Then when you do replace a converter, dont be cheap.
Get a good quality replacement.
If it's not lasting you at least 3-4 years, you need something better.