Is the 1 a new replacement for the 3?

Does it offer a different value proposition .. (i.e. gas mileage, handling, cheaper)?

The 1 and the 3 are different body styles with the 1 being smaller. The 1 offers two inline sixes that produce 230 and 300 hp. Probably the same engine in the 3 series. Base price for the 1 starts at 29k and of course goes up, way up. Maybe about a five or six thousand dollar difference in a compatible 3 series.

1 series is smaller, slightly cheaper than 3 series, and no, not a replacement

The 1 series is the smallest BMW you can buy. It is a compact coupe.

The 3 series is a midsized sedan and coupe.

The 1 series did not replace the 3 series.
The 1 series has been sold in Europe for many years.

The 1 series is cheaper, but it comes with the same engines as the 3 series.

No, the 1-Series is very small, while the 3-Series is kind of bigger, not by much. The 1-Series will drive more like a Mini Cooper with a bigger engine. BMW is trying to fill every niche out there with the new X6 which I think is going to flop, it just looks stupid.

the bmw 1 series is the new entry level bmw, it lacks some of the luxuries, some of the extra room in the back seat
and it gets rid of 2 doors of the 3 series
however, bmw are marketing it as a muscle car and it is much quicker than the 3 series because it is so much lighter.
http://www.goldenstatecars.com/

To correct the guy above me, the Z4 is the smallest BMW you can buy.

The 1 series and the 3 series share a lot of common parts, but the 1 series is smaller and lighter than the 3 series.

If the 1 series and 3 series have the same engine, trans, suspension package, and tires, the 1 series will outperform the 3 series while getting more MPGs.