It does sound like you are doing some kind of HIT routine which works very well if you your intensity is high enough. Doing low amounts of total reps requires you to work very hard for a short time to see results. I personally see great gains doing HIT. One of the advantages to working to failure is it is very easy to track results and see how often you as an individual need to work out. I have found that about 6 times a month gives me the best gains in strength. I started 3 times a week and everytime I reduce the frequency of my workout my strength gains increase.
As far as free weights or machines are concerned, both will provide great results if you work with enough intensity. If you want to get good at lifting barbells by all means do so but you can get just as good of results with machines and they are safer especially when working to failure.