vcf files must be bgzip compressed and tabix indexed. having said that:

vcf-compare *.vcf.gz will output some summary stats

vcf-compare -g *.vcf.gz will output the previous summary stats plus genotype stats (summary, proper comparison, allele frequency and depth)

vcf-compare -p prefix *.vcf.gz will plot these stats, generating prefix*.gp and prefix*png files

you can also use the faster htslib implementation of bcftools instead of vcftools, using bcftools stats and plot-vcfstats.