The clockspeed and IPC creep on the Celerons make them more powerful than they were for previous generations. During the Sandy Bridge era, G530s and G540s were the chips available to non-Microcenter buyers, and they were clocked at 2.3 and 2.4 GHz, respectively.
The Skylake chips cost the same but are clocked at 2.8, 2.9 GHz. What would have cost $70-90 upon release of the Sandy Bridge Celerons now costs only $45.
My guesstimate is that the Skylake Celeron would approximately be the equivalent of a 3.3-3.5 Sandy Bridge dual-core. I assuming slightly over 100 Mhz clock bump to approximate the processing gains over each generation, starting from Sandy Bridge.
Well, if you look carefully... each new generation of Core CPU has somewhere between roughly 5-10% IPC bump. (Closer to 5% than 10%, for most software.)
But also for "marketing" reasons, I suspect, the rated clock speed of each successive generation of Celeron CPU has received a 1-multiplier / 100-Mhz clock-speed bump.
So the IVB Celeron G1610 was 2.6Ghz, HSW Celeron G1820 was 2.7Ghz, and SKL Celeron G3900 is 2.8Ghz.
At least, from memory, that's how I think that they stack up.
And the price of each of those has hovered between $40-45 at most retailers.
That's quite a bit of value at the low-end. Sure, it's not a powerhouse for gaming (much), or video-editing, but it's perfectly adequate for most desktop tasks.
Plus, it's a lot better than the 1.6Ghz C2D Pentium dual-core E2140 CPUs. Although, those could easily be overclocked to twice their default frequency on the right boards. Only now, with Z170 SKY OC and SKL CPUs, have we been able to do the same thing.