thoughts on bike fit....
First off, Kona, don't get discouraged on mountain biking,. unfortunately it seems you picked a bike that fit well physically in the store but does not come close to meeting your expectations on the trail. It happens more often than you think and is one of the biggest reasons newbies will give up on the sport.
To me, when it comes to bike fit for mountain bikes geometry is only the first part of the equation. Much more goes into how a bike rides and feels to you. Many aspects are physical including frame angles, tube lenths ect. The scale weight of a bike is highly overrated, unless you are a top tier road weanie or xc racer. when it comes to weight, the overall balance of a bike and the rotating weight of the wheels make the biggest difference. the most important factor of all is the weight and fitness of the ass in the saddle. Frame material can make a significant difference, especially in hard tails and rigids (though i don't think it matters at all in full susp bikes). Everybody has an opinion, but low to mid range aluminum has always felt dead to me. The gussets and such on modern aluminum bikes dont really change the ride much, they just keep the joints together longer. Butting and manipulation of the tubes is how you get better ride qualities out of any material. Sometimes it is just plain mental. During my shop years i tried just about everything that came through the door in my size and hated far more bikes than I liked.
Based on your comments and others posted IMHO there are a few things to look at as to why the giant just doesn't work for you.
I think comparing the giant to your dear departed Kona is a mistake, at least as equivelent bikes. The Kona was a high mid-range bike in 1996. The component spec was much better, the rotating weight of the wheels was much lighter and it was a pretty supple steel frame, especially for its price point. The bike also had a more performance oriented geometry. The giant is at the upper end of the entry level, therefore components will be heavier across the board, especially the wheels and fork. Being an entry level bike, the ride position will be more comfort orientated than performance orientated. Because of this the bike simply will not handle the same, regardless of new vs old. Geometry hasn't changed as much as everyone seems to think. The biggest difference in a 1996 bike vs 2010 is the head angle, which thanks to long travel forks are much slacker these days. Top tubes are generally longer and stems shorter, but old kona's had relatively long cockpits. most hardtails still have similar seat angles, stay lengths and bottom bracket heights.
Because this is more of an entry level bike, the fork is pretty much just a springy boat anchor and likely hinders more than it helps.
To give you a personal anecdote, I have owned and put significant miles on 4 hardtails in the years that I have been riding. The first I wont mention because it was killed in a tragic accident. I then rode a hardrock for several years taking it places and doing things an entry level bike isn't meant to do. At the time I loved it, but I knew it was holding me back even though I upgraded the snot out of it. After college I moved up to my current hard tail (fat chance buckshaver, still going strong at 15). A few years ago I decided to pull the ol' hardrock out off mothballs to set it up as a single speed (semi horizontal drops) In spite of setting up the cockpit with a very similar position to my other hardtails I could not stand the bike anymore. It was heavy, slow and the feel was all wrong when compared to the Fat. I also owned a late 90's steel rockhopper which with its much more aggressive charecteristics compared to the hardrock was a great bike to hammer on when I felt the need to ride rigid.
I think in this case, this modern bike just isn't what the brain and body need. If I were in your shoes I would not sink alot into upgrades and would probably sell. To get a fork and lighter wheels that might make the bike feel better you will easily spend another few hundred dollars. Put that and the sale proceeds towards a higher end ride. There really is a HUGE difference between a high entry level bike and a good mid range bike. If you really want to go back to the good 'ol days, I frequently used to see older Konas on both the Eugene and Portland craigs list. Also, don't be afraid to explore the used market in general, lots of nice mid range bikes can be had for a bargin. Test ride alot of bikes, there is a lot of parity amung mid range bikes but there are some gems out there.
Regardless don't give up on the sport, but don't be afraid to say enough is enough with this ride, If you don't like it now chances are that you still won't several hundred dollars of upgrades later.
Good Luck!